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Effects of weight on bit on torsional stick-slip vibration of oilwell drill string
Liping Tang,Xiaohua Zhu,Xudong Qian,Changshuai Shi 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.10
The stick-slip phenomenon is a type of dysfunction detrimental to the drilling operation. Field application shows that stick-slip phenomenon is inclined to appear when using a large Weight on bit (WOB). In this paper, effects of the WOB on the stick-slip vibration are investigated. Based on a lumped torsional pendulum model of the drilling system, equation of motion of the drill bit is obtained. By using parameters commonly used in field applications, the bit dynamics are analyzed and the stick-slip vibrations are discussed. During the stick-slip motions, the negative damping effect occurs in the transition from the stick phase to the slip phase. With the increasing WOB, the bit behavior may change from the stable motion to the stick-slip vibration once the WOB reaches the critical value. In case of stickslip vibration, the phase trajectory ultimately converges to a limit cycle which represents periodical bit motion. With increases in the WOB, the limit cycle enlarges. For cases without stick-slip vibrations, the drill bit vibrates damply and finally converges to a state of uniform motion. The results presented in this paper can be applied to interpret some of the field phenomena related to WOB.
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Analysis of mechanical behavior and hysteresis heat generating mechanism of PDM motor
Changshuai Shi,Xiaohua Zhu,Juan Deng,Liping Tang 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.3
Positive displacement motor (PDM), which is prone to high temperature fatigue failure, can be weakened in its application in deep and superdeep well. In order to study the forced state, deformation regularity and thermal hysteresis of PDM motor, the paper established the three-dimensional thermal-mechanical coupled Finite element model (FEM). Based on the theoretical research, experimental study and numerical simulation, the study found that the displacement of stator lining shows a sinusoidal variation under internal pressure, when adapting the general form of sine function to fitting inner contour line deformation function. Then the paper analyzed the hysteresis heat generating mechanism of the motor, learning that hysteresis thermogenous of stator lining occurs due to the viscoelastic of rubber material and cyclic loading of stator lining. A heartburn happens gradually in the center of the thickest part of the stator lining as temperature increases, which means work efficiency and service life of PDM will be decreased when used in deep or superdeep well. In this paper, we established a theory equation for the choice of interference fit and motor linetype optimization design, showing hysteresis heat generating analyzing model and method are reasonable enough to significantly improve PDM’s structure and help better use PDM in deep and surdeep well.
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Qian He,Xiaohua Chen,Tang Wu,Liyuan Li,Xiaofan Fei 대한신경과학회 2019 Journal of Clinical Neurology Vol.15 No.1
Background and Purpose There is conflicting evidence in the literature on the association between benzodiazepines (BDZs) and the risk of dementia. This meta-analysis aimed to determine the relationship between the long-term usage of BDZs and the risk of dementia. Methods The PubMed and Embase databases were systematically searched for relevant publications up to September 2017. The literature search focused on observational studies that analyzed the relationship between the long-term use of BDZs and the risk of dementia. Pooled rate ratios (RRs) with 95% confidence interval (CI) were assessed using a random-effects model. The robustness of the results was checked by performing subgroup and sensitivity analyses. Results Ten studies were included: six case–control and four cohort studies. The pooled RR for developing dementia was 1.51 (95% CI=1.17–1.95, p=0.002) in patients taking BDZ. The risk of dementia was higher in patients taking BDZs with a longer half-life (RR=1.16, 95% CI= 0.95–1.41, p=0.150) and for a longer time (RR=1.21, 95% CI=1.04–1.40, p=0.016). Conclusions This meta-analysis that pooled ten studies has shown that BDZ significantly increases the risk of dementia in the elderly population. The risk is higher in patients taking BDZ with a longer half-life (>20 hours) and for a longer duration (>3 years).
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Disparity-based Error Concealment for Stereoscopic Images with Superpixel Segmentation
( Yizhang Zhang ),( Guijin Tang ),( Xiaohua Liu ),( Changming Sun ) 한국인터넷정보학회 2018 KSII Transactions on Internet and Information Syst Vol.12 No.9
To solve the problem of transmission errors in stereoscopic images, this paper proposes a novel error concealment (EC) method using superpixel segmentation and adaptive disparity selection (SSADS). Our algorithm consists of two steps. The first step is disparity estimation for each pixel in a reference image. In this step, the numbers of superpixel segmentation labels of stereoscopic images are used as a new constraint for disparity matching to reduce the effect of mismatching. The second step is disparity selection for a lost block. In this step, a strategy based on boundary smoothness is proposed to adaptively select the optimal disparity which is used for error concealment. Experimental results demonstrate that compared with other methods, the proposed method has significant advantages in both objective and subjective quality assessment.
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Jihui Yao,Jiapeng Jiao,Ruiqiang Liu,Fei Zha,Xiaojun Guo,Xiaohua Tang,Haifeng Tian,Yue Chang 한국화학공학회 2021 Korean Journal of Chemical Engineering Vol.38 No.7
To improve the dispersion of metals and to enhance the catalytic performance of SAPO-34 molecular sieves, the template-assisted method was applied to synthesize Co, Ni and Zn modified SAPO-34 molecular sieves by using palygorskite as silicon source and tetraethylammonium hydroxide as template. The metal modified SAPO-34 molecular sieves were characterized by XRD, SEM, XPS, N2-adsorption-desorption, NH3-TPD, FTIR, ICP-AES and TG. The N atoms of tetraethylammonium hydroxide exhibited the different forces to three metal ions, thus the acidity of the molecular sieves was further regulated. Compared with metal modified SAPO-34 molecular sieves prepared by impregnation, metal modified SAPO-34 molecular sieves prepared by template-assisted maintained higher surface area, bigger pore volume and better dispersion of metals. The catalytic performance of metal modified SAPO-34 molecular sieves prepared by template-assisted method in the reaction of methanol-to-olefins (MTO) was investigated in the fixed bed reactor. Under the reaction conditions that the reaction temperature was 400 oC, the reaction pressure was 0.1 MPa, the feed WHSV was 2.0 h1 and the mass of catalyst was 0.5 g, Ni modified SAPO-34 molecular sieves exhibited great methanol conversion and high selectivity to light olefins. The selectivity of light olefins reached 95.7%.
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